strip whitespace
use -moz-hyperlinktext for links
remove custom button styling
use rgba(0,0,0,0.25) for all shadows
remove more custom button styling
Use threedcolor for most borders

this is also what is used in thunderbird's default theme.
Unfortunately, this will not change with the system theme.
use #888a85 for secondary text

see comment on previous commit
rm custom font families
rm duplicate code
use black/white for quickreply textarea

unfortunately I did not find a way to use thunderbird default colors for this
use a bunch of -moz-* colors
add :focus selectors when :hover is used
change some colors in quick reply header
fix quickreply label line-height
Fixup "use a bunch of -moz-* colors"
Revert "remove more custom button styling"

This reverts commit 53cf5283af6992d59af51c0baced3a4a69e2a002.
Fix flat button colors
Fix button height
replace tabs by spaces
Fix footer color

footer backgrounds are transparent grey. This way it works with both
light and dark themes.